Dust flux, Vostok ice core

Dust flux, Vostok ice core
Two dimensional phase space reconstruction of dust flux from the Vostok core over the period 186-4 ka using the time derivative method. Dust flux on the x-axis, rate of change is on the y-axis. From Gipp (2001).

Saturday, January 15, 2011

Self organization in geological phenomena, part 2: stone and soil stripes

Today the World Complex travels to Antarctica (via the wayback machine, to 1993). (Maps were prepared for some presentation given at about that time).

At the end of the Antarctic peninsula (around 60 W and north of the Antarctic circle) there is a grouping of islands called the South Shetland Islands.

One of the South Shetland Islands is called King George Island. It is dotted with research bases, including Marsh Station and Ferraz Station. The Brazilians had a research base within Admiralty Bay serviced by a naval vessel called the Barão de Teffé.

Brazilian research vessel Barão de Teffé in Admiralty Bay (viewed from shore).

I spent six weeks in the field with a team of Brazilians on a site near Mazurek Point. It was one of the best-supplied field camps I've ever experienced (only Ice Island was better supplied, but the Brazilians outdid us Canadians by supplying abundant--really abundant--wine and chocolate).

Six of us at Marsh Station (the seventh, Jefersòn, took the picture). 
I am at the left, along with Paulo dos Santos, Antonio Rocha-Campos, 
Roland Trompette (famed for his West African work), Ricardo (our mountaineer), 
and Alexandre Uhlein.

 Iceberg with supply helicopter for scale, viewed from our base camp.

The goal of the project was to study the Polonez Cove Formation, which mainly consisted of interbedded diamictites, turbidites and volcaniclastic flows of Oligocene Age. Actually, at the time, the age hadn't been completely established.
The base camp was set up on Low Head (that little x near the bottom of the map). Most of the areas of interest were in the numbered sites along the coast running up the right edge of the map.

Wypianski icefall, which will play a role in a later posting, pretty much covered up anything of interest. The interesting rocks were exposed along the coast from Low Head, across Mazurek Point and on up to Lions Rump at the top of the map.

But that irregular area marked SSSI (site of special scientific interest) was off-limits to us, as it was a sea lion breeding area. Unfortunately, there was a very interesting geological transition close to the boundary, where we found a series of stacked debris flows interbedded with turbidites intercalated with a series of volcaniclastic flows coming in from another direction.

But geology sometimes has to yield to biology.

Luckily, we went in summer.

The snow cover was ephemeral. When the snow disappeared, on a slope not far from the base camp you would see these . . .

Soil stripes near Low Head, KGI.

They weren't actually a target of our study, and to be honest, we didn't know what they were. What we observed looked like ripples, with alternations between gravel and lichen- or moss-covered silt. They were oriented perpendicular to the slope and were consistent in thickness and composition over a distance of tens of metres.

Details of soil stripes

Further upslope where the debris was much coarser (fresh angular cobbles), there were similar, albeit larger structures.

Stone stripes, KGI.

I had originally thought this to be a form of fluting, however all of these rocks, which have been shed from the ridge at the top right of this photo, are actually lying on top of ice, albeit a long way down. This patterning is formed by a succession of freeze-thaw cycles, which result in sorting the rocks as they move downlope. Similar images can be seen here.

Formal explanation for these features was published in Nature in 1993, so I had a nice read when I got back home.

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